Turbine nozzle vane construction



May 8, 1962 E. w. RADTKE 3,033,519

TURBINE NOZZLE VANE CONSTRUCTION Filed Sept. 12, 1958 f l/VVEN TOR ZEDWARD W RADTKE A 7'7'ORNEY r M". n

United States Patent TURBINE NOZZLE VANE CONSTRUCTION Edward W. Radtke,Bloomfield, Conn., assignor to United Aircraft Corporation, EastHartford, Conn., a corporation of Delaware Filed Sept. 12, 1958, Ser.No. 760,582 1 (Ilaim. (Cl. 25352) This invention relates toturbomachinery and more particularly to the nozzle vane arrangementimmediately upstream of the turbine.

In turbines which are intended to drive a compressor or the like wherethe speed or load on the turbine must be controlled, the nozzles leadingto the turbine buckets may beof variable geometry. These variablegeometry nozzle passages can be provided by means of a plurality ofvanes which are pivotable so as to alter the configuration of thepassages therebetween. With these pivoted vanes it is necessary toadequately seal the free ends of the vanes so as to avoid leakage of airaround the tips of the vanes.

It is therefore an object of this invention to provide a sealingarrangement for pivoted nozzle vanes whereby just the right amount ofsealing force is provided thus avoiding excessive friction andexcessively high torque necessary for pivoting the vanes.

These and other objects of this invention will become readily apparentfrom the following detailed description of the drawing in which:

FIG. 1 is a side elevation of a turbine-compressor arrangement withportions partly broken away to show the turbine nozzle vane arrangement;

FIG. 2 is an enlarged detailed partial cross section of the nozzle vanearrangement and its sealing mechanism;

FIG. 3 is a partial cross section taken along the line 33 of FIG. 2; and

FIG. 4 is a partial cross section taken along the line 44 of FIG. 1.

Referring to FIG. 1 a turbine casing is shown which houses turbineblades or buckets 12. The blades or buckets 12 are connected to asuitable shaft for driving a compressor housed within the casing 14 orother load. Air under pressure enters the toroid or volute 16 where itis ducted through an annular passage 18. The flow then moves radiallyinwardly toward the axis of turbine rotation past a plurality of nozzlevanes 20. The nozzle vanes 20 are peripherally spaced about the turbinebuckets 12 and each includes a pivot shaft 22 which lies su stantiallyparallel to the axis of rotation of the turbine.

As seen in FIGS. 2 and 3, each of the turbine blades 26 is arranged suchthat a nozzle passage is for-med between adjacent blades. By rotatingeach of the vanes 2% about their pivot shaft 22 the geometry of thepassage 24 therebetween can be varied to provide suitable flow into theturbine blades. Thus, the driving force on the turbine can be controlledin accordance with any desired schedule.

As seen in FIGS. 2 and 4, each of the nozzle vanes 20 and the pivotshaft 22 includes a spline 26 which has mounted thereon a gear segment28. Each of the gear segments 28 is operatively connected to a ring gear30 so that upon rotation of the ring gear 30 all of the nozzle vanes 20will be simultaneously pivoted about their shafts 22 thereby varying thegeometry of each of the nozzle passages 24 therebetween.

As best seen at the top of FIG. 1, one of the vanes 20 has a masterpivot shaft 34 suitably connected by a yoke 36 to an actuating pistonrod 38. The piston rod 38 may be controlled by mechanism such as shownin US. Patent No. 2,752,858 to Berges, or US. Patent No. 2,651,492 toFeilden. Motion of the rod 38 rotates the master pivot 34 which throughthe ring gear 30' rotates all the remaining segmental gears 28 and therespective vanes.

In very small turbine compressor units, as for example for aircraft airconditioning assemblies, the actuating force for pivoting the nozzlevanes must be at a minimum. However, at the same time it is necessarythat a good seal be provided at the free ends of the nozzle vanes 20 sothat there will be a minimum amount of leakage around the ends of theblades. Such leakage reduces the performance of the machine. In order toprovide an adequate seal for the free ends of the nozzle vanes 20, anannular pressure plate 40 (see FIGS. 1 and 2) is provided which engages,the outer free ends of all of the nozzle vanes 20. The pressure plate 40fits into an annular recess 42 and also includes inner and outer sealingrings 44 and 46 which engage the inner and outer walls of the annularrecess 42. A light spring 48 may be provided to provide a nominalpressure for holding the plate 40 against the outer ends of the nozzlevanes 20. However, when there is a flow of air through the nozzlepassages 24 formed by the vanes 20, there is a negative pressuregradient or distribution pattern in a downstream direction through thepassage 24 which gradient is due both to the shape of the nozzle and thepressure drop existing between the inlet and the outlet of the turbine.

In any event, when there is flow there will be a pressure gradient.Since there exists along the flow path a pressure gradient or pressuredistribution, it is immaterial that the nozzles are pivoted because thenew passageway will also exhibit a pressure gradient or distributionalong its flow path. This pressure tends to push the plate 40 away fromthe outer ends of the nozzle vanes 20. In order to insure proper seatingof the pressure plate against the ends of the vanes 20, one or morepressure taps 50 are provided in the pressure plate 40 so that apredetermined air pressure will be established behind the pressure plate40. Since there is a pressure drop in a downstream or cho-rdwisedirection past the vanes 20, the location of the taps 50 along this flowpath is chosen so that the pressure at this location, established behindthe pressure plate 40 provides a total force greater than the totalforce tending to push the plate 40 away from the vanes 20. The net forceis just sutficient to insure an adequate sealing engagement of thepressure plate 40 with the ends of the vanes 20. In this manner thefriction caused by the pressure plate engaging the vanes 20 is notexcessive yet the force is sufiicient to insure adequate sealingthroughout the operating range of the turbine.

In reality, the point at which the pressure is picked oif and fed behindthe pressure plate is a compromise condition which will exert a force onthe plate to give substantially its optimum operating range. Thus, itcan be seen that the force of the plate pressing against the nozzleswill differ for every position of the nozzles, i.e., from its full opento its full closed position.

As a result of this invention a very simple yet highly efficient sealingmechanism has been provided which insures positive sealing of the endsof turbine nozzle vanes while avoiding excessive torque requirements.

Although only one embodiment of this invention has been illustrated anddescribed herein, it will be apparent that various changes may be madein the construction and arrangement of the various parts withoutdeparting from the scope of the novel concept.

What it is desired by Letters Patent is:

In a radial entry turbomachine having a rotor having an axis, bladesdisposed about the periphery of said axis carried by said rotor, aplurality of vanes surrounding said blades and forming a plurality ofradial entry nozzle passages for directing fluid under pressure againstsaid blades for driving said rotor, said passages having a shaft whichinduces a negative pressure gradient in the flow therethrough, saidvanes having their spans running parallel to said axis, a pivot shaftcarried by one spanwise end of each of said vanes and being parallel tothe span, means for rotating said shafts and varying the geometry ofsaid nozzle passages, an annular plate having one side engaging theother spanwise ends of said vanes and having a sealing engagementtherewith to define one end wall of said nozzle passages, said platebeing in a plane transverse to said axis, a channel having radiallyinner and outer walls and receiving said plate, said plate and channelforming a substantially closed chamber on the other side of said plate,seal means carried adjacent the inner and outer peripheral edges of saidplate and engaging the walls of said chamber, and means for conductingfluid under pressure from at least one of said nozzle passages into saidchamber to create a force on the other side of said plate to provide asealing engagement between said one side of said plate and said vanes,including a duct leading to one of said nozzle passages and terminatingat a point between the leading and trailing edge of the adjacentrespective vane, said duct terminating at a point located along the flowin said nozzle passage wherein the average pressure of said fluid willprovide a total force on said other side of said plate which is slightlyin excess of that necessary to maintain a sealing engagement between theplate and the adjacent vane during flow through the nozzle passages.

References Cited in the file of this patent UNITED STATES PATENTS2,651,496 Buckland et a1. Sept. 8, 1953 2,733,853 Trumpler Feb. 7, 19562,770,943- Beale NOV. 20, 1956 2,976,013 Hunter Mar. 21, 1961 FOREIGNPATENTS 88,257 Sweden Jan. 5. 1937

